(A) Field of the Invention
The present invention is related to a method of an optimizing radiation pattern of a smart antenna. Specifically, it can come true SDMA (Space Division Multiple Access) of smart antennas.
(B) Description of Related Art
In tradition, wireless communication at the same base station has been separated by frequency such as FDMA (Frequency Division Multiple Access); by time such as TDMA (Time Division Multiple Access); or by code such as CDMA (Code Division Multiple Access). Smart antennas add a new method of separating users by space through SDMA.
Usually, base station antennas using an omnidirectional or sectored radiation pattern cause power waste in unexpected direction and interference for the other users. A smart antenna system, a perfect idea to solve the problem, can suppress interferences by placing nulls in the antenna pattern in the directions of the interfering sources for co-channeling and adjusting the directions of main lobes toward the users.
Facing the advanced demand for wireless mobile communications, the use of smart antenna exploits spatial diversity to further improve spectral efficiency. Basically, a smart antenna is an array antenna combined via a beamforming network (amplitude and phase control network). The beamforming network can be implemented in either RF-circuitry, real-time digital signal processing hardware, or in a hybrid solution.
The benefits of smart antennas include lower power consumption, intersymbol interference reduction, signal and interference ratio increment, range extension, higher data rate support, and ease of integration into the base station system. The capacity of a system is limited by co-channel interference. Smart antennas can offer the spatial allocation of multiple mobile users to a co-channel using the technique of Spatial Division Multiple Access (SDMA) with its spatial separation ability, thereby increasing the system capacity.
More specifically, the benefits derived from a smart antenna system are described as follows: (a) interference rejection: smart antennas can suppress the interferences generated by other user signals of the co-channel via the pattern nulling technique; (b) multipath rejection: smart antennas can place nulls on multipath and put main lobes toward the users to solve the multipath problem; (c) better coverage: focusing the energy sent into the cell increases the base station coverage. Lower power requirement also makes a battery life longer for a handset; (d) increasing capacity: the spatial allocation at a co-channel is an efficient method to increase the capacity of cellular radio networks by smart antenna systems; (e) reducing expense: owing to better coverage, less base station request, lower amplifier costs and lower power consumption will result; and (f) increasing signal power gain: the signal power gain will be increased because input signals from antenna elements are combined to optimize available power.
To sum up, smart antenna technology can effectively improve wireless system performance. It can work in operators of personal communication system (PCS), cellular and wireless local loop (WLL) networks. Moreover, the smart antenna system is also applicable to all major wireless protocols and standards.